1. Field of the Invention
The present invention concerns the monitoring of a plurality of hydraulic, pneumatic or electro-mechanical actuators combined inside a given functional unit.
This unit is typically a postal sorting machine comprising a large number of identical electromagnets allocated to a given function for which it is extremely difficult to date to carry out a detailed effective check as part of preventive maintenance. The same applies for units containing identical pneumatic or hydraulic actuators.
2. Description of the Related Art
A method and device to test a plurality of electric actuators is described in the document WO97/20224. In this system, a plurality of sensors are allocated to each actuator whose measurements are transformed into signals with an identification code. The identified signals are then received in a data processing system where they are compared with nominal values.
When a signal deviates from a nominal value, the information given means that the actuator issuing the signal is defective. This system is cumbersome as first of all a plurality of sensors is provided for each actuator and secondly a set of sensors is required for each actuator.
The invention is the outcome of a solution research to effectively resolve this problem.
It consists of a monitoring and diagnostic device relating to a plurality of identical actuators characterised in that it includes the following stages:
successively and separately feeding each of said plurality of identical actuators, from a given electric, pneumatic or hydraulic energy source and in similar circuit conditions;
establishing for each actuator a reading or curve of the flow measured according to the time;
establishing a superposition from all said curves and defining a track occupied by the largest number and considered in this respect as a normality track;
isolating the curves having deviations relating to said track; and
establishing an anomaly diagnostic of each isolated curve on the basis of the deviation(s) it has with said track.
Said superposition can be embodied with the entire part of each of said curves, in which case the period of excitation of the actuators shall be identical for all. It could also be embodied with the significant portions of these curves, in which case the excitation period could vary from one actuator to another.
Depending on whether the actuators are to be electric, pneumatic or hydraulic components, the flow measured shall respectively be a current, a flow of compressed air or a flow of hydraulic liquid.
In practice, it is inevitable that the nominal flows or currents (current or flow recorded in a permanent state under feed) of the various actuators vary slightly within a tolerance range. Before the superposition stage, it would therefore be advantageous to apply a homothetic transformation of each curve so as to bring the value of the detected nominal flow or current down to a selected average value. Of course, prior to this operation, a first examination could have been carried out so as to mark and analyse the nominal current defects (value detected outside said range).
The invention also concerns devices for implementing the method defined above, devices able to be integrated in units or machines comprising the elements to be monitored, or even include independent diagnostic tools.